Tissue paper is a lightweight paper that can be used to prepare absorbent products such as bath tissue, facial tissue, and absorbent towels. Tissue paper is generally prepared by forming a wet web of cellulosic fibers and transferring the web to a heated cylinder called a Yankee dryer to reduce the moisture content. The tissue paper is subjected to a creping process where the sheet is dried to a desired moisture level, and mechanically removed from the Yankee dryer by contacting a blade against the dryer.
At the interface between the Yankee dryer surface and the tissue web resides a thin film called a Yankee coating. The surface of the Yankee dryer is generally coated with a chemical additive such as a polymer. The chemical additive attaches the paper to the surface of the Yankee dryer, whereby the paper is creped by the creping blade. The chemical additive serves to protect both the surface of the Yankee dryer and the creping blade because, during the creping process, the blade contacts the polymer layer instead of scratching the metal surface of the Yankee dryer. Generally, the Yankee coating comprises chemical additives that are capable of facilitating efficient sheet transfer and desirable adhesion properties as well as provide protection for the surface of the Yankee dryer. Commonly used chemical additives include polyaminoamide-epichlorohydrin resins and polyvinyl alcohol.
The creping process directly affects the quality of the tissue paper product. Many of the properties of tissue are influenced by the creping process, including softness, bulk, stretch, and absorbency. There is a continuing need for improved Yankee coatings that enhance machine runnability, improve tissue product properties, and protect the dryer surface.